Why we are interested in radiocarbon

The most spectacular work that is done on the field is probably melting every day 1 ton of ice in a huge vacuum chamber. Back in the lab, the released air from the ice will be analyzed for its radiocarbon content, which has fundamental implications for dating purposes and identification of sources of atmospheric carbon.

Picture of the melting chamber on the field

The big melting chamber on Taylor Glacier with a capacity to melt 1 ton of ice at once. Micheal is just taking care on the chamber during the melting process (see the flames underneath). [credit: Micheal Dyonisius, University of Rochester]

Radiocarbon, or C14, is a rare radioactive carbon isotope with a half-life time of 5730 years. Because carbon is found in almost all natural products, the activity of C14 in a material can be used to trace back the time when the carbon was built in that material. This basic concept lies behind the widely used C14 dating method (but works also with other radionuclides) und builds probably the most prominent dating technique for natural materials.

Not only dating is an application of C14, but also can we use it as an identifier of sources of atmospheric carbon at a specific point in time. In the application in our field work, C14 in methane (CH4) is measured and used to figure out whether the CH4 came from a recently formed archive (i.e. biosphere sources such as tropical and boreal wetlands) or an archive that has been sealed away from the atmosphere for very long time (i.e. carbon in the deep ocean and permafrost). For example, if C14 in CH4 drops during an event when the CH4 concentration is increasing, we know it must come from an “old” source, and vice versa.

Picture of filling the melting chamber

Vas and Micheal are filling up the melting chamber with one core piece just drilled near by. About 14 of these cores fit in the chamber. [credit: Micheal Dyonisius, University of Rochester]

One motivation to investigate this in the past is that the current human-made warming has potential to destabilize some old sources such as permafrost and clathrate hydrates and, hence, add to the release of greenhouse gases emitted by human activity. This so called positive feedback could have taken place in the past for example during the last glacial transition when the global climate changed from the last ice age to the current warm period. By identifying such events and their links to natural climate change, we can better asses by how much we have to take this effect into account for the current warming event.

The group from the University of Rochester around Vas Petrenko that leads this project (which is by the way also the flagship project of our field work), is the first group ever that analyses C14 of CH4 in trapped air in polar ice, and also managed to significantly improve the precision for C14 in CO2 and CO with their methodology. The reason for their significant step forward in the analytics lies in the large amount of ice/air from the same time period it can be taken from Taylor Glacier. At normal ice core drill sites the ice layering is horizontal and only a limited amount of ice is available for a certain time, whereas at Taylor Glacier the layering is vertical which allows accessing basically unlimited amount of ice from the same time period.

In a previous work done a couple of years ago, the team of Rochester could show that during a specific event about 12’000 years age, an “old” source was clearly active. In the current campaign they want to extend their C14 record on a much larger time span and also try to rule out an inherent problem to C14 in air from polar ice samples: production of C14 in the ice itself (in-situ production).

More details about the interesting work of the University of Rochester group can be obtained from their blog.

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2 Comments on “Why we are interested in radiocarbon

    • That’s exactly what the work on Taylor Glacier is looking at. If large amounts of methane have been released in the past from these permafrost sources (or other methane hydrate forms such as found on the ocean basin) we should see its fingerprints in the C14 data. So far the evidence from the past goes more towards that these sources are fairly stable and don’t release gases so fast.


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